1. Field of the Invention
The present invention relates to a sulfur-based photosensitive member. More particularly, the present invention relates to a sulfur-based photosensitive member wherein a form of sulfur which is physically changeable on absorbing the energy of light is used as a photosensitive material.
2. Description of the Prior Art.
Heretofore, various materials such as silver halides, diazo compounds, organic elemental compounds, or photosensitive resins, etc. have been used as the photosensitive material for photosensitive members. The photosensitive members prepared using these materials are expensive since the production cost of these materials is high. Moreover, the starting materials of photosensitive materials, such as silver, are in short supply at the present time and their prices are soaring worldwide and thus they are not suitable for producing photosensitive members of low cost. Furthermore, since some starting materials are poisonous, problems of pollution in producing the photosensitive members tend to occur.
Conventional photosensitive members have various advantages such as high sensitivity, capability to reproduce a half-tone image, etc. However, even though a photosensitive member is deficient in its qualities, e.g., the sensitivity, image properties, etc., are not improved to the level attained with conventional photosensitive members, if the photosensitive member is sensitive to the extent that it can be used with copying machines on the market without difficulty and moreover if a line copy of the member is possible although a half-tone copy is not possible, it is commercially usable in some fields of application. A diazo photosensitive member is an example of such a photosensitive member. A diazo photosensitive member, however, also is high in cost. In actuality, the advantage of this type of photosensitive member resides in its low cost.
Without going into great detail, at the present time, petroleum is consumed in a large amount and the refining of petroleum is carried out with large sized machines on a large scale. At the desulfurizing stage, a large amount of sulfur is by-produced and the supply of sulfur now exceeds its demand. Thus, an important area of interest is how to effectively use the excessive sulfur, since sulfur will necessarily cause environmental pollution.
Heretofore, it has been reported that sulfur has 30 or more allotropic forms, but with the exception of certain specific forms, their structures and properties have not been clarified. With regard to the photoproperties of sulfur, only the facts that sulfur undergoes photopolymerization in solution; that on irradiating sulfur in the solid state with .alpha.-rays, .beta.-rays, .gamma.-rays, or ultraviolet rays, a radioactive sulfur of a short life is produced; that sulfur is photoconductive; and that on heat-melting, sulfur undergoes phase changes and reaches a supercooled condition, etc. are known. Of these findings, the photoconductivity and the ability to achieve a supercooled condition are utilized in a process for forming an image. That is, the following methods are described in U.S. Pat. No. 2,297,691. One method comprises forming a thin layer of sulfur on a support by melting and cooling, placing the thin layer in a dark place, applying an imagewise exposure to the layer when the electric resistance of the layer has sufficiently increased, to thereby form an image due to the difference in the electric resistance of the thin layer, charging the non-exposed area where the electric resistance is high, and then adhering electrostatically colored powders onto the above area to thereby form a visible image. Another method comprises forming a crystalline sulfur layer on a support, heating the layer in an imagewise manner to thereby imagewise melt the layer so as to cause a phase change and supercooling therein and then adhering powder on the area to thereby form a visible image.
However, since the sensitivity of the sulfur layer used is low and for various reasons, neither of these processes have been commercialized.
In view of the present situation of sulfur as a starting material and the development situation with respect to specific applications, the fields of application of sulfur have not yet been opened up. Upon investigation of new fields utilizing sulfur, it has now been found that certain kinds of sulfur possess photosensitivity and undergo material and constructional variation on absorbing the energy of light, thereby changing their physical properties.